Ceramic materials and particularly structural ceramic materials generally have a high resistance to corrosion and erosion. This is true of e.g. several oxides, nitrides, carbides and borides. Also, said materials have no toxic properties. When used as implant materials said materials are completely inactive, i.e. neither positive nor negative reactions with surrounding tissues take place, and consequently it is possible to attain a biological integration to bone tissue without any intermediate connective tissue. Such materials are termed inert when used as implant materials. These properties make several oxides, nitrides, carbides and borides potentially very valuable as inert dental and orthopedic implant materials.
However, it is desirable that materials having a favorable biocompatibility are not only inert, i.e. able to fasten mechanically to a bone tissue, but also bioactive, i.e. the implant can be bonded chemically to a bone tissue. Oxides, nitrides, carbides and borides do not have this property. On the other hand it is known that phosphate-based materials, having a chemical composition similar to the "inorganic" or "ceramic" matter in bone tissue, can display bioactive properties. Such a phosphate-based material is e.g. hydroxylapatite, Ca(PO.sub.4).sub.3. However, a synthetic hydroxylapatite has a low tensile toughness and hence a low strength and also a tendency to gradually develop a continuous crack growth. Another example of a bioactive material having a calcium phosphate-base is tricalcium phosphate Ca.sub.3 (PO.sub.4).sub.2, but this compound has an unsatisfactory strength. Also, it has a not negligible water solubility and consequently may be dissolved before the bond to the bone tissue has developed. Thus, in this respect, hydroxylapatite is preferred as compared to tricalcium phosphate.